CC2650 disconnects shortly after app starts

I am working with Raspberry Pi2 and Windows 10 IoT Core.
After runing aplication, I recieve some  lux updates(cca. 3-4) , but after that, sensor tag gets disconnected (green LED blinking). However it doesn't get unpaired from Raspberry. If I start the app again, it works again 3-4 times and get disconnected again. 

Here is my code:

async void initialize()
{
    Debug.WriteLine("Running...");

    var luxDevices = await DeviceInformation.FindAllAsync(GattDeviceService.GetDeviceSelectorFromUuid(new Guid("F000AA70-0451-4000-B000-000000000000")));
    if(luxDevices.Count == 0)
    {
        Debug.WriteLine("No devices found...");
        return;
    }
    var luxService = await GattDeviceService.FromIdAsync(luxDevices[0].Id);
    if(luxService == null)
    {
        Debug.WriteLine("No lux service...");
    }
    var luxData = luxService.GetCharacteristics(new Guid("F000AA71-0451-4000-B000-000000000000"))[0];
    luxData.ValueChanged += lux_ValueChanged;
    await luxData.WriteClientCharacteristicConfigurationDescriptorAsync(GattClientCharacteristicConfigurationDescriptorValue.Notify);

    var luxConfig = luxService.GetCharacteristics(new Guid("F000AA72-0451-4000-B000-000000000000"))[0];
    writer.WriteByte((Byte)0x01);
    await luxConfig.WriteValueAsync(writer.DetachBuffer());
    Debug.WriteLine("Config done, awaiting data...");
}

async void lux_ValueChanged(GattCharacteristic sender, GattValueChangedEventArgs args)
{
    Debug.WriteLine("Lux value update...");
}

Can you give me some tips or guidance to work this problem out?

Thanks in advance!